Throttle control in internal combustion engine for noise reduction

ABSTRACT

Limitation of the opening rate of the throttle valve is prohibited unless the following conditions have been all satisfied: (i) the engine speed detected at starting opening the throttle valve is below a prescribed speed; (ii) the throttle angle detected at starting opening the throttle valve is below a prescribed throttle angle; (iii) the target throttle-open angle is above a prescribed throttle-open angle; and (ix) the target opening rate of the throttle valve is above a prescribed opening rate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to throttle control in aninternal combustion engine. More specifically, it relates to throttlesystem and method enabling reduction of air-flow noise occurring inresponse to changes in the amount of the throttle opening.

2. Description of the Related Art

As is widely known, the quantity of air supplied to an internalcombustion engine (will be referred to as “engine” where appropriate) isadjusted at a throttle valve provided in an intake passage of theengine. When the throttle valve quickly opens, it disturbs the flow ofair so that the air starts swirling. Such swirl airflow may sometimecause specific noise (will be refereed to as “throttle inflow noise”).Meanwhile, an intake manifold forms one portion of the intake passage,and it is known that a resin-made intake manifold is now increasinglyused. Such a resin intake manifold, however, inevitably allows theabove-stated throttle inflow noise to be easily propagated or emit tothe outside.

To counter this, for example, a known method provides a net or plate inthe intake passage to regulate the flow of air downstream of thethrottle valve and thereby reduce throttle inflow noise. However, thismethod involves drawbacks of reduced engine output due to increased airresistance within the intake passage, increased weight, increasedproduction cost, etc. Also, this method is not effective enough toreduce the throttle inflow noise when a resin made intake manifold isused for the reason already mentioned.

In view of the above, another method has been proposed which reducesthrottle inflow noise by limiting a rate at which the throttle valveopens (will be referred to as “throttle opening rate”) below a specificlimit rate under given conditions so that the throttle valve opensrelatively slowly (see Japanese Laid-opened Patent Application No.2001-98958, No. 2001-234758). For example, Japanese Laid-opened PatentApplication No. 2001-98958 proposes opening the throttle valve at alower rate when the throttle angle is smaller than a specific value.

Although it is true that the throttle inflow noise can be reduced byopening the throttle valve at a reduced rate as described above,lowering the throttle opening rate may deteriorate the controllabilityof the engine output.

SUMMARY OF THE INVENTION

In view of the above situation, the present invention has been made toprovide a throttle system and throttle control method for an internalcombustion engine enabling reducing throttle inflow noise caused by thethrottle valve being opened while minimizing deterioration of thecontrollability of the engine output.

To achieve the above object, a first aspect of the invention relates toa throttle system for an internal combustion engine including a throttlevalve, accelerating means operated by an operator to adjust an engineoutput of the internal combustion engine, and throttle valve controllingmeans for controlling the throttle valve to open in accordance with themanner in which the accelerating means has been operated. The throttlevalve controlling means is adapted to execute under given conditions athrottle opening rate limitation limiting a throttle opening rate atwhich the throttle valve is opened, below a limit opening rate. Thisthrottle system also includes engine speed detecting means for detectingan engine speed of the internal combustion engine, and the throttlevalve controlling means prohibits the throttle opening rate limitationif the engine speed detected via the engine speed detecting means atstarting opening the throttle valve is above a prescribed engine speed.

A research of the inventors has revealed that throttle inflow noise doesnot occur unless the throttle valve quickly opens where the engine speedis lower than a specific speed. Therefore, the throttle system of thefirst aspect has the foregoing structure to avoid the throttle openingrate being unnecessary limited when no or almost no throttle inflownoise is likely to occur. Thus, it is possible to reduce throttle inflownoise advantageously while minimizing deterioration of thecontrollability of the engine output.

In another form of the invention, it is preferable that engine torquedetecting means for detecting engine torque of the internal combustionengine be provided, and that the throttle valve controlling means befurther adapted to prohibit the throttle opening rate limitation if theengine torque detected via the engine torque detecting means at startingopening the throttle valve is above a prescribed engine torque.

The research of the inventors also revealed that throttle inflow noisedoes not occur unless the throttle valve quickly opens where themagnitude of the engine torque is lower than a certain level. Therefore,the foregoing structure of the throttle system improves the reliabilityin avoiding the throttle opening rate being unnecessary limited when noor almost no throttle inflow noise is likely to occur, and this leads toa further improvement in the effect of reducing throttle inflow noisewhile minimizing deterioration of the controllability of the engineoutput.

In another form of the invention, it is preferable that throttle openingamount detecting means for detecting an opening amount of the throttlevalve be provided, and that the throttle valve controlling means befurther adapted to prohibit the throttle opening rate limitation if theopening amount of the throttle valve detected via the throttle openingamount detecting means at starting opening the throttle valve is above aprescribed opening amount.

As aforementioned, throttle inflow noise does not occur unless thethrottle valve quickly opens where the engine torque is below a certainlevel, and it is possible, as is widely known, to determine themagnitude of the engine torque based on the opening amount of thethrottle valve. Therefore, the foregoing structure of the throttlesystem further improves the reliability in avoiding the throttle openingrate being unnecessary limited when no or almost no throttle inflownoise is likely to occur, and this leads to a further improvement in theeffect of reducing throttle inflow noise while minimizing deteriorationof the controllability of the engine output.

In another form of the invention, it is preferable that the throttlevalve controlling means be further adapted to (I) determine based on themanner in which the accelerating means has been operated whether thethrottle valve is required to open quickly and (ii) prohibit thethrottle opening rate limitation if the throttle valve is not requiredto open quickly.

Throttle inflow noise does not occur unless the throttle valve opens ata rate higher than a certain level. Therefore, the foregoing structureof the throttle system further improves the reliability in avoiding thethrottle opening rate being unnecessary limited when no or almost nothrottle inflow noise is likely to occur, and this leads to a furtherimprovement in the effect of reducing throttle inflow noise whileminimizing deterioration of the controllability of the engine output.

In another form of the invention, it is preferable that the throttlecontroller be further adapted to (i) determine a target throttle-openamount by which the throttle valve is required to open and a targetthrottle opening rate at which the throttle valve is required to openbased on the manner in which the accelerating means has been operated,and (ii) prohibit the throttle opening rate limitation if the targetthrottle-open amount is below a prescribed throttle-open amount or ifthe target throttle opening rate is below a prescribed opening rate.

It is not necessary to execute the throttle opening rate limitation ifthe throttle body is not required to open quickly. Therefore, theforegoing structure of the throttle system further improves thereliability in avoiding the throttle opening rate being unnecessarylimited when no or almost no throttle inflow noise is likely to occur,and this leads to a further improvement in the effect of reducingthrottle inflow noise while minimizing deterioration of thecontrollability of the engine output.

In another form of the invention, it is preferable that the throttlecontrolling means be further adapted to (i) determine whether theopening amount of the throttle valve is changing across a predeterminedrange thereof, and (ii) prohibit the throttle opening rate limitation ifthe opening amount is not changing across the predetermined range.

The research of the inventors also revealed that throttle inflow noisedoes not occur unless the throttle opening amount is changing across acertain range. Therefore, the foregoing structure of the throttle systemfurther improves the reliability in avoiding the throttle opening ratebeing unnecessary limited when no or almost no throttle inflow noise islikely to occur, and this leads to a further improvement in the effectof reducing throttle inflow noise while minimizing deterioration of thecontrollability of the engine output.

A second aspect of the invention relates to a throttle system for aninternal combustion engine, including a throttle valve, acceleratingmeans operated by an operator to adjust an engine output of the internalcombustion engine, and throttle valve controlling means for controllingthe throttle valve to open in accordance with the manner in which theaccelerating means has been operated. The throttle valve controllingmeans executes under given conditions a throttle opening rate limitationlimiting a throttle opening rate at which the throttle valve is opened,below a limit opening rate. Further, in this throttle system, thethrottle valve controller is adapted to (i) determine whether thethrottle opening amount is changing across a predetermined rangethereof, and (ii) prohibit the throttle opening rate limitation if thethrottle opening amount is not changing across the predetermined range.

A third aspect of the invention relates to a method for controlling athrottle valve of an internal combustion engine. This method includes(i) executing under given conditions a throttle opening rate limitationlimiting a throttle opening rate at which the throttle valve is opened,below a limit opening rate, and (ii) prohibiting the throttle openingrate limitation if an engine speed detected at starting opening thethrottle valve is above a prescribed engine speed.

A fourth aspect of the invention relates to a method for controlling athrottle valve of an internal combustion engine. This method includes(i) executing under given conditions a throttle opening rate limitationlimiting a throttle opening rate at which the throttle valve is opened,below a limit opening rate, and (ii) prohibiting the throttle openingrate limitation if an opening amount of the throttle valve is notchanging across a predetermined range thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and/or further objects, features and advantages of theinvention will become more apparent from the following description ofpreferred embodiments with reference to the accompanying drawings, inwhich like numerals are used to represent like elements and wherein:

FIG. 1 is a view schematically showing the configuration of a throttlesystem according to one exemplary embodiment of the invention;

FIG. 2 is a graph illustrating a region in which throttle inflow noiseoccurs, defined by the values of engine speed and engine torque detectedat starting opening a throttle valve;

FIG. 3 is a graph illustrating the relationship between the engine speeddetected at starting opening the throttle body and the throttle angle atwhich throttle inflow noise occurs while the throttle body is beingopened;

FIG. 4 is a flowchart showing one exemplary routine for determiningwhether to execute the throttle opening rate limitation;

FIG. 5 is a flowchart showing one exemplary routine for limiting thethrottle opening rate (i.e., throttle opening rate limitation); and

FIG. 6 is a timechart illustrating one example for explaining theoperation of the throttle control system of the exemplary embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EXEMPLARY EMBODIMENTS

Hereinafter, a throttle system for an internal combustion engine inaccordance with one exemplary embodiment of the invention will bedescribed with reference to the accompanying drawings.

FIG. 1 is a view schematically showing the configuration of the throttlesystem of the exemplary embodiment. Referring to FIG. 1, the throttlesystem is provided with a throttle valve 10 disposed along an intakepassage of the internal combustion engine (will be simply referred to as“engine”). The air drawn via an air duct, not shown, into the intakepassage passes through a throttle body 11 of the throttle valve 10, asurge tank, and an intake manifold, both not shown, and is finallyintroduced into each combustion chamber.

As well as the throttle body 11, the throttle valve 10 includes athrottle motor 12 and a throttle sensor 13. The shaft of the throttlebody 11 is coupled to the throttle motor 12, and the throttle sensor 13is disposed near the same shaft.

The throttle motor 12 drives the throttle body 11 to change its angle(will be referred to as “throttle angle”). More specifically, the angleof the throttle body 11 is changed so as to adjust the sectional area ofthe intake passage and thus change the flow rate of the air flowingtherethrough. Namely, this changes the rate at which air is supplied tothe engine. The throttle sensor 13 measures the angle of the throttlebody 11 (throttle angle θ).

The throttle system includes an ECU (Electronic Control Unit) 14governing the operation of the throttle valve 10. The ECU 14 includes anCPU for executing various programs to control the throttle valve 10, amemory storing those programs, input and output communication ports eachoutputting or receiving various signals from/to external elements.

In this exemplary embodiment, as well as the throttle sensor 13, thethrottle system includes various other sensors, such as an engine speedsensor 15 for detecting the speed of the engine (engine speed NE) and anaccelerator sensor 13 for detecting the amount an accelerator 17 isoperated by an operator (accelerator operation amount ACCP). Suchsensors are all connected to the above-stated input communication portof the ECU 14 so that the ECU 14 receives signals from them. The outputcommunication port of the ECU 14, on the other hand, is connected to thethrottle motor 12 so that the ECU 14 controls the throttle valve 10.

In operation, the ECU 14 computes a target throttle angle θ based on theengine speed NE detected via the engine speed sensor 15 and theaccelerator operation amount ACCP detected via the accelerator sensor17. Then, the ECU 14 controls the throttle motor 12 such that the actualthrottle angle θ matches the target throttle angle θt computed. In thisexemplary embodiment, the throttle angle θ (i.e., rotational angle ofthe valve shaft of the throttle body 11) is 0 degree when the throttlebody 11 is fully closed and increases as the throttle body 11 rotatesfrom that closed position.

The inventors of the present invention conducted a research regardingthrottle inflow noise caused by the throttle angle being changed, andthey discovered that throttle inflow noise dose not always occur whenthe throttle angle changes quickly unless some other conditions are alsosatisfied. More specifically, throttle inflow noise does not occurunless the throttle body 11 quickly opens where the engine speed (enginespeed NE) is below a prescribed speed (engine speed NE1) (condition A)and the engine torque (engine torque TR) is below a prescribed toque TR1(condition B).

FIG. 2 is a graph illustrating a region in which occurrence of throttleinflow noise has been acknowledged during the research, which is definedby the engine speed NE and the engine torque TR detected at startingopening the throttle body 11. In FIG. 3, the curve WOT represents themaximum value of the engine toque TR that is correlative with the enginespeed NE.

As evident from the graph, whether throttle inflow noise occurs largelydepends on the values of the engine speed NE and engine torque TR atstarting opening the throttle body 11. That is, throttle inflow noisedoes not occur unless the throttle valve quickly opens with the aboveconditions A, B both satisfied, i.e., with the engine speed NE beingbelow NE1 and the engine torque TR being below TR1.

For example, the magnitude of the engine torque TR generated at aspecific engine speed may be obtained as a function of the throttleangle θ. In this case, therefore, the above-stated condition B may bemodified to “throttle angle θ is below a predetermined angle θ1”(condition B′).

In the case of the internal combustion engine used in this exemplaryembodiment, according to the result of the research, throttle inflownoise occurs when the throttle body 11 quickly opens at an engine speed(NE) lower than 3000 rpm and a throttle angle (θ) smaller than 9degrees.

FIG. 3 is a graph illustrating the relationship between the engine speedNE detected at starting opening the throttle body 11 and the throttleangle θ at which throttle inflow noise occurs while the throttle body 11is opening. In this graph, the solid line curve represents the throttleangle θ at which throttle inflow noise occurs when the throttle body 11quickly opens from the fully closed position, whereas the dotted linecurve represents the throttle angle θ at which throttle inflow noiseoccurs when the throttle body 11 quickly opens where the engine torque(TR) is at its upper limit value within a range causing throttle inflownoise.

Referring to FIG. 3, even if the throttle body 11 opens where theabove-stated conditions A, B are both satisfied, throttle noise will notoccur unless the throttle angle θ is within a specific range thereof.That is, throttle inflow noise only occurs when throttle angle θ ischanging across a range from a lower limit angle θa to a upper limitvalue θb, and this range of throttle angle θ will hereinafter bereferred to as “noise range.” In this exemplary embodiment, the lowerlimit angle θa is 20 degrees while the upper limit angle θb is 30degrees.

As described above, throttle inflow noise only occurs under suchspecific conditions. Thus, the noise can be reduced sufficiently even ifthe opening rate of the throttle body 11 is limited to a limit valueonly when those conditions have been satisfied. By thus restrictinglimitation of the throttle opening rate, it is possible to avoiddeterioration of the controllability of the engine output which mayotherwise be caused by the throttle opening rate being limitedunnecessarily.

To avoid such unnecessary limitation of the throttle opening rate,therefore, the ECU 14 determines whether to execute the throttle openingrate limitation as follows. Hereinafter, a control executed by the ECU14 to limit the opening rate ω of the throttle body 11 below a specificlimit value will be referred to as “throttle opening rate limitation”.First, the ECU 14 determines if conditions a, b have been satisfied. Thecondition a requires the engine speed NE detected at starting openingthe throttle body 11 be less than a prescribed engine speed NE1 whichis, for example, set to 3000 rpm. The condition b requires the throttleangle θ detected at starting opening the throttle body 11 be smallerthan a prescribed angle θ1 which is, for example, set to 9 degrees. Ifeither condition is not satisfied, the ECU 14 prohibits the throttleopening rate limitation.

In addition, the ECU 14 also determines if the manner in which theaccelerator 16 has been operated requires the throttle body 11 to openquickly. At this time, the ECU 14 refers to changes in the acceleratoroperation amount ACCP. Through such determination, it becomes clearwhether the throttle body 11 is required to open quickly. If not, theECU 14 prohibits the throttle opening rate limitation.

In this exemplary embodiment, the ECU 14 determines whether the throttlebody 11 is required to open quickly by evaluating conditions c, d. Thecondition c requires that a target throttle-open angle Δθt be above aprescribed angle Δθ1, while the condition d requires a target throttleopening rate ω be above a prescribed rate ω1. The target throttle-openangle Δθt is an angle by which the throttle body 11 is required to open,and this angle is determined based on the manner in which theaccelerator 16 has been operated. Likewise, the target throttle openingrate ωt is a rate at which the throttle body 11 is required to open, andthis rate also is determined based on the same manner. The manner inwhich the accelerator 16 has been operated may be defined by, forexample, the amount or rate of increase in the accelerator operationamount ACCP, and will be referred to as “accelerator operation manner”where appropriate.

As aforementioned, the ECU 14 does not carry out the throttle openingrate limitation if the throttle angle θ detected at starting opening thethrottle body 11 is below the prescribed angle θ1 (condition b). Alongwith this, the ECU 14, when evaluating condition c, determines whetherthe target throttle angle θt is above a prescribed throttle angle θ2(=θ1+Δθ1).

Even if the above conditions have been all satisfied, however, the ECU14 does not carry out the throttle opening rate limitation, namely doesnot limit the opening rate ω to a limit opening rate ω2 unless thethrottle angle is within the above-stated noise range (θa<θ<θb). Thatis, the ECU 14 simply opens the throttle body 11 at a rate required bythe accelerator operation manner regardless of whether the conditions a,b, c, d have been all satisfied if the throttle angle θ is out of thenoise range. The limit opening rate ω2 may preferably be set as large aspossible within a range where throttle inflow noise can be reduced to anallowable level.

The flowchart of FIG. 4 represents one exemplary routine executed by theECU 14 to determine whether to execute the throttle opening ratelimitation. The ECU 14 repeats this routine as a subroutine atpredetermined intervals.

Referring to FIG. 4, the ECU 14 first determines in step S100 whetherthe target throttle angle θ is larger than the present throttle angle θ.This step refers to whether the throttle body 11 is now required toopen.

If NO in step S100, namely if it is required to close or maintain thethrottle body 11, the ECU 14 then resumes a normal throttle control instep S140 so that the present throttle angle θ will be maintained orreduced as needed. In this normal throttle control, the ECU 14 simplycontrols the throttle angle θ in accordance with the acceleratoroperation manner.

If YES in step S100, namely if it is now required to open the throttlebody 11, the ECU 14 then executes steps S110 to 130 to see if each ofthe conditions a, b, c, d is satisfied. Here, step S110 determineswhether the engine speed NE is below the prescribed speed NE1 (conditiona), and step S120 determines whether the throttle angle θ is below theprescribed angle θ1 (condition b), and step S130 determines whether thetarget throttle angle θt is above the prescribed angle θ2 (condition c)and whether the target opening rate ωt of the throttle body 11 is abovethe prescribed rate ω1 (condition d).

If any one of the above conditions is not satisfied, the ECU 14 proceedsto step S140 to resume the normal throttle control. When the conditionshave all been satisfied, conversely, the ECU 14 then proceeds to stepS150 to carry out the throttle opening rate limitation, as will bedescribed later.

The flowchart of FIG. 5 represents one exemplary routine of the throttleopening rate limitation. Referring to FIG. 5, the ECU 14 firstdetermines in step S200 whether the present throttle angle θ detectedvia the throttle sensor 13 is within the noise range (θa<θ<θb). If YES,the ECU 14 then determines whether the target throttle opening rate ωtis above the limit opening rate ω2.

If the ECU 14 determines “NO” in either step above, it proceeds to stepS230 and sets the throttle opening rate ω to the required opening rateωt. If the ECU 14 determines “YES” in both steps, conversely, itproceeds to step S220 and sets the throttle opening rate ω to the limitopening rate ω2.

After the throttle opening rate ω has been set as above, the ECU 14finishes the routine temporarily and drives the throttle motor 12 suchthat the throttle body 11 opens at the throttle opening rate ω thus set.

FIG. 6 is a timechart illustrating one example for more clearlyexplaining the operation of the throttle control system of the exemplaryembodiment. In this example, the accelerator 16 is first operated attime t1 thus requiring the throttle body 11 to open.

This example starts from time t1 where the engine speed NE is below theprescribed speed NE1 (condition a satisfied) and the throttle angle θ isbelow the prescribed angle θ (condition b satisfied). First, theaccelerator 16 is operated at time t1 in a manner satisfying theabove-stated conditions c, d.

Subsequently, the throttle angle θ starts increasing at time t2 inresponse to the accelerator 16 operated from time t1. At this time, thethrottle angle θ changes at a rate corresponding to the acceleratoroperation manner.

Then, in response to the throttle angle θ reaching the lower limit ofthe noise range at time t3, the throttle opening rate ω is then limitedto the limit opening rate ω2. This limitation of the throttle openingrate ω continues until the throttle angle θ exceeds the upper limit ofthe noise range at time t4.

At time t4, the throttle opening rate ω is again increased at a ratecorresponding to the accelerator operating manner, and the throttleopening rate ω thus increased is maintained until the throttle angle θreaches the target throttle angle θt at time t5.

Below are described advantages obtained with the throttle systemdescribed above:

(1) Since limitation of the throttle opening rate ω is prohibited whenthe engine speed NE is above the prescribed speed NE1, the throttleopening rate ω is not unnecessarily limited when throttle inflow noiseis not likely to occur. Thus, it is possible to adventurously avoidthrottle inflow noise while minimizing deterioration of thecontrollability of the engine output.

(2) Since limitation of the throttle opening rate ω is carried out onlywhen the engine speed NE is below the prescribed speed NE1 and thethrottle angle θ is smaller than the prescribed angle θ1 (i.e., theengine toque TR is small). This improves the advantage of avoidingunnecessary limitation of the throttle opening rate.

(3) Limitation of the throttle opening rate ω is also prohibited whenthe required throttle open angle Δθ is below the prescribed angle Δθ1and the target throttle opening rate ωis below the prescribed openingrate ω1. In this way, limitation of the throttle opening rate ωisavoided in the case where the throttle body 11 is to be slowly openedand thus no or almost no throttle inflow noise will occur. This leads toa further improvement in the effect of avoiding unnecessary limitationof the throttle opening rate.

(4) Limitation of the throttle opening rate ω is also prohibited unlessthe throttle angle θ is changing across the noise range (θa<θ<θb), inother words. This leads to a further improvement in the effect ofavoiding unnecessary limitation of the throttle opening rate.

Hereinafter, some examples of modifications which may be made to thethrottle system of the above exemplary embodiment will be described.

(a) While the ECU 14 makes the determination as to the engine torque TRby referring to the throttle angle θ in step S120 of FIG. 4, the ECU 14may instead refer to other parameter that is correlative to the enginetorque TR.

(b) While the ECU 14 makes the determination in step S130 of FIG. 4based on the required throttle-open angle Δθ and the target throttleopening rate ωt, it may instead use other parameters as long as whetherthe throttle body 11 is required to open quickly can be appropriatelydetermined. For example, the accelerator operation amount ACCP or theincrease amount or rate of the target throttle angle θt may be utilizedas such parameters.

(c) While the ECU 14, in the procedure shown in FIG. 5, carries outlimitation of the throttle opening rate only when the throttle angle θis changing across the noise range, other condition for carrying out thelimitation may be applied. That is, throttle inflow noise can be reducedwhile avoiding unnecessary limitation of the throttle opening rate ifexecution of the throttle opening rate limitation is restrictedaccording to specific conditions determined using the engine speed NEdetected at starting opening the throttle body 11, etc.

(d) The ECU 14 may skip step S130 of FIG. 4. Even in this case, sincethe throttle opening rate limitation is prohibited depending on theengine speed NE and the throttle angle θ as described above, unnecessarylimitation of the throttle opening rate is advantageously avoided.

(e) The ECU 14 may skip step S120 of FIG. 4. Even in this case, sincethe throttle opening rate limitation is prohibited depending on theengine speed NE and the necessity to open the throttle body 11 quickly,unnecessary limitation of the throttle opening rate is advantageouslyavoided.

(f) The ECU 14 may skip both the above two steps. Even in this case,since the throttle opening rate limitation is prohibited depending onthe engine speed NE, unnecessary limitation of the throttle opening rateis advantageously avoided.

(g) The ECU 14 may skip the whole routine shown in FIG. 4 and onlyexecute the routine shown in FIG. 5. Even in this case, since limitationof the throttle opening rate is prohibited unless the throttle angle θis within the noise region, it is possible to reduce throttle inflownoise while avoiding unnecessary limitation of the throttle opening ratewhich may lead to deterioration of the controllability of the engineoutput.

While the invention has been described with reference to preferredembodiments thereof, it is to be understood that the invention is notlimited to the preferred embodiments or constructions. To the contrary,the invention is intended to cover various modifications and equivalentarrangements other than described above. In addition, while the variouselements of the preferred embodiments are shown in various combinationsand configurations, which are exemplary, other combinations andconfigurations, including more, less or only a single element, are alsowithin the spirit and scope of the invention.

1-7. (canceled)
 8. A method for controlling a throttle valve of aninternal combustion engine, comprising: executing under given conditionsa throttle opening rate limitation limiting a throttle opening rate atwhich the throttle valve is opened, below a limit opening rate; andprohibiting the throttle opening rate limitation if an engine speed ofthe internal combustion engine detected at starting opening the throttlevalve is above a prescribed engine speed.
 9. A method as set forth inclaim 8, further comprising: prohibiting the throttle opening ratelimitation if an engine torque of the internal combustion enginedetected at starting opening the throttle valve is above a prescribedengine torque.
 10. A method as set forth in claim 8, further comprising:prohibiting the throttle opening rate limitation if an opening amount ofthe throttle valve detected at starting opening the throttle valve isabove a prescribed opening amount.
 11. A method as set forth in claim 8,further comprising: prohibiting the throttle opening rate limitation ifthe throttle valve is not required to open quickly.
 12. A method as setforth in claim 8, further comprising: determining a target throttle-openamount by which the throttle valve is required to open and a targetthrottle opening rate at which the throttle valve is required to open;and prohibiting the throttle opening rate limitation if the targetthrottle-open amount is below a prescribed throttle-open amount or ifthe target throttle opening rate is below a prescribed opening rate. 13.A method as set forth in claim 8, further comprising: prohibiting thethrottle opening rate limitation if an opening amount of the throttlevalve is not changing across a predetermined range thereof.
 14. A methodfor controlling a throttle valve of an internal combustion engine,comprising: executing under given conditions a throttle opening ratelimitation limiting a throttle opening rate at which the throttle valveis opened, below a limit opening rate, and prohibiting the throttleopening rate limitation if an opening amount of the throttle valve isnot changing across a predetermined range thereof.
 15. A throttle systemfor an internal combustion engine, comprising: a throttle valve; anaccelerator operated by an operator to adjust an engine output of theinternal combustion engine; an engine speed detector for detecting anengine speed of the internal combustion engine; and a throttle valvecontroller that is adapted to: control the throttle valve to open inaccordance with a manner in which the accelerator has been operated,execute under given conditions a throttle opening rate limitationlimiting a throttle opening rate at which the throttle valve is opened,below a limit opening rate, and prohibit the throttle opening ratelimitation if the engine speed detected via the engine speed detector atstarting opening the throttle valve is above a prescribed engine speed.16. A throttle system as set forth in claim 15, further comprising anengine torque detector for detecting an engine torque of the internalcombustion engine, wherein the throttle valve controller is furtheradapted to prohibit the throttle opening rate limitation if the enginetorque detected via the engine torque detector at starting opening thethrottle valve is above a prescribed engine torque.
 17. A throttlesystem as set forth in claim 15, further comprising a throttle openingamount detector for detecting an opening amount of the throttle valve,wherein the throttle valve controller is further adapted to prohibit thethrottle opening rate limitation if the opening amount of the throttlevalve detected via the throttle opening amount detector at startingopening the throttle valve is above a prescribed opening amount.
 18. Athrottle system as set forth in claim 15, wherein the throttle valvecontroller is further adapted to: determine based on the manner in whichthe accelerator has been operated whether the throttle valve is requiredto open quickly, and prohibit the throttle opening rate limitation ifthe throttle valve is not required to open quickly.
 19. A throttlesystem as set forth in claim 15, wherein the throttle controller isfurther adapted to: determine a target throttle-open amount by which thethrottle valve is required to open and a target throttle opening rate atwhich the throttle valve is required to open based on the manner inwhich the accelerator has been operated, and prohibit the throttleopening rate limitation if the target throttle-open amount is below aprescribed throttle-open amount or if the target throttle opening rateis below a prescribed opening rate.
 20. A throttle system as set forthin claim 15, wherein the throttle controller is further adapted to:determine whether the opening amount of the throttle valve is changingacross a predetermined range thereof, and prohibit the throttle openingrate limitation if the opening amount is not changing across thepredetermined range.
 21. A throttle system for an internal combustionengine, comprising: an accelerator operated by an operator to adjust anengine output of the internal combustion engine; a throttle valve; and athrottle valve controller that is adapted to: control the throttle valveto open in accordance with the manner in which the accelerator has beenoperated, execute under given conditions a throttle opening ratelimitation limiting a throttle opening rate at which the throttle valveis opened, below a limit opening rate; determine whether the throttleopening amount is changing across a predetermined range thereof, andprohibit the throttle opening rate limitation if the throttle openingamount is not changing across the predetermined range.